Spark ignition (SI) engines, wherein fuel and air are provided to a cylinder and ignited by a spark, have conventionally been provided with fuel and air by either carburetion or by fuel injection. In fuel injection, one or more injectors squirt fuel into the cylinder(s) of the engine, and/or into the cylinder air intake port(s), with the object of atomizing the fuel and mixing it with the air to better enable ignition of the fuel. In carburetion, fuel is supplied into the intake airstream entering the engine and its cylinders, generally at a venturi (a necked passage) which generates suction to pull fuel into the intake airstream in accordance with the flow rate of the intake airstream. Since the air/fuel mixture has a major impact on engine performance and pollutant emissions, the goal of both carburetion and fuel injection is to attain the desired fuel-air mixture at the desired time within the engine cylinder(s). Carburetion systems have the advantage of being rather easily and inexpensively manufactured, but they have the disadvantage that they offer only crude control over the degree of air/fuel mixing, the air/fuel ratio, and the timing of the air/fuel charge entering the cylinder(s). As a result, carburetors tend to offer lesser fuel economy and greater pollutant emissions than fuel injection systems, which is why many modern SI engines (e.g., automotive SI engines) use fuel injection. However, in some applications—in particular for small engines (which are typically regarded as engines having an output of less than 25 horsepower)—carburetion is still commonly used simply because the cost of implementing fuel injection in small engine applications (e.g., lawnmowers, snowthrowers, chainsaws, and other small tools and vehicles) would increase their costs to levels unaffordable to many consumers. Thus, small engines have a reputation (often deserved) for being “dirty” and inefficient. It would therefore be useful to have means available for efficiently and economically enhancing carburetion quality so as to reduce these disadvantages.